1. Field of the Invention
The present invention relates to light-emitting diode (LED) illumination circuits, illumination devices, and liquid crystal display (LCD) apparatuses having a protection function for open-circuit failure.
2. Description of the Related Art
LEDs are now replacing cold cathode fluorescent lamps (CCFLs) for use in backlights of LCD apparatuses to achieve an extended color range, reduced power consumption, and reduced amounts of environmentally unfriendly substances. A long CCFL can be used for a backlight of a large-screen LCD apparatus, which uses a large illumination area (the area that the backlight can illuminate). The CCFL may be powered from both ends thereof. On the other hand, LEDs utilize light emission from, for example, a semiconductor chip about 1 mm square. If LEDs are used, the number of LEDs used is increased for larger illumination areas, and the LEDs are connected in series for power supply.
LEDs used for backlights of LCD apparatuses no longer illuminate in the event of failures, including the end of service life. The failures of LEDs are broadly divided into three modes: (1) open-circuit failure due to breaks, (2) short-circuit failure, and (3) decreased light intensity.
A variety of attempts have been made to prevent such failures. For example, Japanese Unexamined Patent Application Publication No. 2002-335012 discloses an LED based on a technique against open-circuit failure. This LED includes a light-emitting element and a semiconductor protective element connected in parallel therewith to electrically protect the light-emitting element. The light-emitting element includes a light-emitting layer formed of a nitride semiconductor containing at least gallium. The protective element becomes conductive either in a forward direction or in a reverse direction at an applied voltage above the forward voltage of the light-emitting element.